Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint 06/98

Spectral analysis of O(He)-type post-AGB stars

T. Rauch(1), S. Dreizler(1) and B. Wolff(2)

(1)Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(2)Institut für Theoretische Physik und Astrophysik der Universität, D-24098 Kiel, Germany

accepted by Astronomy & Astrophysics

Abstract. We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations.
In the spectra of HS 1522+6615 we discovered a variability of the O VI 5290Å line complex on a time scale of few days. We also report on the discovery of a ring structure in the planetary nebula K 1-27 which has an O(He)-type central star.
We discuss how the group of O(He) stars fits in our picture of hydrogen-deficient post-AGB stellar evolution.

Key words: Stars: abundances - Stars: atmospheres - Stars: evolution - Stars: individual: HS 1522+6615, HS 2209+8229 - Stars: AGB and post-AGB - planetary nebulae: individual: GJJC 1, K 1-27, LoTr 4

Paper (717k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 06-Aug-1998